As is known, conventional rotary tablet-making machines comprise a rotary turntable which carries near its periphery an annular series of die cavities in which the dies are clamped. Above and below the die turntable are upper and lower punches carried for rotation with the turntable, there being one upper and one lower punch for each die cavity. The heads of the punches may be guided by raising and lowering camming surfaces to control their reciprocating movements into or out of the die cavities as the die turntable rotates through filling, weight adjusting, compression and ejection stations all spaced around the single turntable.
The production rate of a prior art machine of the type described above is limited by the diameter of the rotary die turntable and its speed of rotation. Furthermore, such presses have relied upon gravity feed of free-flowing materials in order to obtain uniform tablet weight, hardness and size. The gravity flow system often affects the mechanical production rate of the tablet press, the tablet weights, hardness, friability and resultant disintegration time. Furthermore, prior art tablet presses utilizing the aforesaid type die turntable generally require that a lubricant be mixed into the product to be compressed. This is sometimes undesirable and sometimes affects the ultimate efficacy of ingredients such as those found in pharmaceuticals, as well as requiring higher pressures to overcome the lack of cohesiveness caused by the addition of lubricant to the product itself. Prior art tablet presses also use close-tolerance bores to guide the upper and lower punches which are actuated by raising and lowering cams. Unless cleanliness and lubrication of the cams and punches are scrupulously observed, stickiness, gumming, binding and scoring of these parts occur; and the punches must be removed frequently for cleaning and relubricating.